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Richard, correct engineering require your amp is able to output square waves at full level indefinitely. No way to undersize power feedback resistance under this point.
What i wanted to lighten is the margin you'll like to add for reasonable temp/distortion in this resistance. Musical Peaks are 12db more than average. (peak meters/vu-meters) and vu-meters are not 0dB all the time. Plus the X1.4 between square and sinus, it makes at least >X5 margin in normal use. Can be enough ? I believe yes, and add that, most of the time, we run our amps way under their max power.
And, if it is PA at full power, who care about hifi ?
Just a though.
In a ideal world, we'll like to size each resistance in the feedback bridge for they reach the same temp for the feedback ratio remain the same, whatever their temp behavior...
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A PA at full power should be hifi ... I heard it done, several times, obviously by people with a few more marbles rattling around up top - so there are no excuses for the normal rubbish ...
Man we are talking of real high end...resistance's distortions in a concert hall, go figure !
After reading about thermal distortion , having the FB "out on a wire" might
be best. I also could return it anywhere I like.
A couple of large resistors(below) "outboard" (with the cap). Lo-Z in CF
would allow this - unlike a VFA.
PS - we don't have to be cheap , like Pioneer.
OS
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Lo-Z , shield them if you like.
As a gross example - the original leach has it's OP's out on" long wires"
It's at Mhz , as well. Still works.
With those to-220 resistors, all can stay firmly planted on the pcb.
OS
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But, is there any thing really wrong with a single 3 w unit (thick film) ?
mouser has them for $.50 -.80 .... http://www.irctt.com/file.aspx?product_id=36&file_type=datasheet
I have option for a 3W or the to-220 already done.
OS
mouser has them for $.50 -.80 .... http://www.irctt.com/file.aspx?product_id=36&file_type=datasheet
I have option for a 3W or the to-220 already done.
OS
Do it the way Bonsai does it... I do it same way, if I understand his description correctly.
Thx-RNMarsh
Yes, I have done that and agree it is a good sounding solution.....voltage coefficients, noise cancellation and/or something, but it does do good things subjectively.
Multiple parallel output stage emitter resistors also.
Dan.
Hi Edmond.
Nice to see a perceptive post on this topic, there has been little discussion of optimisation.
But the Oliver condition that 2*RE = 1/Gm was derived for minimum crossover distortion in class B+ circuits.
It is not obvious to me that it is still optimal in this case, what's your rationale?
Compliments of the season and
Best wishes
David